In battery powered applications such as smartphones, there may be the need for providing voltages that are above or below the battery voltage, e.g. depending on the State Of Charge (SOC) of the battery itself. A typical example is the generation of a constant 3.3V rail from a Li-Ion battery pack, wherein the voltage of the battery pack may vary between 2.5V and 4.2V, depending on the SOC of the battery pack. When the battery is fully charged (4.2V), a step-down regulator is required to generate the 3.3V rail (e.g. a buck converter or an LDO), whilst when the battery is discharged (2.5V) a step-up regulator is needed to generate the same 3.3V output rail (e.g. a boost regulator).
In such a scenario, a buck-boost regulator 100 as shown in FIG. 1 may be used. The regulator 100 comprises two buck switches S1 and S2, at the left hand side of the coil 101, and two boost switches S3 and S4, at the right hand side of the coil 101. Hence, the step-up function and the step-down function are implemented using a single coil 101 as an external component (typically in addition to an input capacitor and an output capacitor of the regulator 100).
A drawback of the topology shown in FIG. 1 is the use of two switches S1 and S3, which are arranged in series between the input and the output of the regulator 100, thereby impacting the efficiency of the regulator 100 at relatively high loads and thereby limiting the maximum current that can be delivered to the output of the regulator 100 in a boost or step-up mode.